C++ - segmentation fault when inheritance

Question

I got very strange behaviour with my very simple example which crashes when i use inheritance (class NapanaApplication : public QGuiApplication), but doesn't crash and works properly when using directly QGuiApplication.

The code is exactly as seen below, the NapanaApplication doesn't do anything, just inherits from QGuiApplication.

What's wrong?

SOLVED: I found a reason. It is because the QGuiApplication takes the argc as reference, but the NapanaApplication constructor doesn't. It doesn't generate any error, but it causes that the QGuiApplication operated with some temporary argc variable instead of the one from main.

main.cpp

#include "napanaapplication.h"
#include "napanawindow.h"

int main(int argc, char* argv[]) {

    /*NapanaApplication app(argc, argv);*/ // segmentation fault

    QGuiApplication app(argc, argv); // no error        

    NapanaWindow win;

    win.resize(800, 600);
    win.show();

    return app.exec();
}

napanaapplication.h

#ifndef NAPANAAPPLICATION_H
#define NAPANAAPPLICATION_H

#include <QGuiApplication>

class NapanaApplication : public QGuiApplication
{

    Q_OBJECT

public:
    explicit NapanaApplication(int argc, char* argv[]);
signals:

public slots:
};

#endif // NAPANAAPPLICATION_H

napanapplication.c

#include "napanaapplication.h"

NapanaApplication::NapanaApplication(int argc, char* argv[]) : QGuiApplication(argc, argv) {}

Output from debugger: it crashes when strlen is called in QString::fromLocal8Bit. The char* pointer on which the strlen is called has value 0x21, i don't understand why, it should be probably something from argv.

0   strlen  /usr/lib/debug/lib/x86_64-linux-gnu/libc-2.19.so    106 0x7ffff65c0aea  
1   QString::fromLocal8Bit  qstring.h   534 0x7ffff7142c11  
2   QCoreApplication::arguments qcoreapplication.cpp    2254    0x7ffff738503d  
3   sm_performSaveYourself  qxcbsessionmanager.cpp  188 0x7ffff05f5e3a  
4   sm_saveYourselfCallback qxcbsessionmanager.cpp  171 0x7ffff05f5cc9  
5   _SmcProcessMessage          0x7ffff014ad37  
6   IceProcessMessages          0x7fffeff3b8c7  
7   QSmSocketReceiver::socketActivated  qxcbsessionmanager.cpp  322 0x7ffff05f67e0  
8   QSmSocketReceiver::qt_static_metacall   qxcbsessionmanager.moc  68  0x7ffff05f6f88  
9   QMetaObject::activate   qobject.cpp 3718    0x7ffff73c097e  
10  QMetaObject::activate   qobject.cpp 3583    0x7ffff73c016c  
11  QSocketNotifier::activated  moc_qsocketnotifier.cpp 134 0x7ffff7458376  
12  QSocketNotifier::event  qsocketnotifier.cpp 296 0x7ffff73cb4db  
13  QCoreApplicationPrivate::notify_helper  qcoreapplication.cpp    1093    0x7ffff7382872  
14  QCoreApplication::notify    qcoreapplication.cpp    1038    0x7ffff7382554  
15  QGuiApplication::notify qguiapplication.cpp 1537    0x7ffff77f3076  
16  QCoreApplication::notifyInternal    qcoreapplication.cpp    965 0x7ffff738245e  
17  QCoreApplication::sendEvent qcoreapplication.h  224 0x7ffff7386087  
18  socketNotifierSourceDispatch    qeventdispatcher_glib.cpp   101 0x7ffff73f6afe  
19  g_main_context_dispatch         0x7ffff4f8dbd4  
20  ??          0x7ffff4f8de18  
21  g_main_context_iteration            0x7ffff4f8debc  
22  QEventDispatcherGlib::processEvents qeventdispatcher_glib.cpp   418 0x7ffff73f7799  
23  QPAEventDispatcherGlib::processEvents   qeventdispatcher_glib.cpp   115 0x7ffff0648906  
24  QEventLoop::processEvents   qeventloop.cpp  128 0x7ffff737f0b2  
25  QEventLoop::exec    qeventloop.cpp  204 0x7ffff737f373  
26  QCoreApplication::exec  qcoreapplication.cpp    1229    0x7ffff7382b36  
27  QGuiApplication::exec   qguiapplication.cpp 1528    0x7ffff77f3026  
28  main    main.cpp    13  0x40275a    

Answer 1

Note the signature of QGuiApplication:

QGuiApplication(int & argc, char ** argv)

Your function has int argc instead. I think you're causing a segfault when the integer value is then treated as a reference by the parent class constructor.